class BaseClass(object):
    url = None

    def __init__(self):
        print 'BaseClass __init__'

    def __del__(self):
        print 'BaseClass __del__'

    def print_url(self):
        print 'url'

class MyClass(BaseClass):

    def __init__(self):
        super(MyClass, self).__init__()
        print 'MyClass __init__'

    def __del__(self):
        print 'MyClass __del__'

instance = MyClass()
instance.url = 'http://www.baidu.com'
print instance.url
